Mantis bugtracker which is a freeware and is actually much more than a bug tracker
It can provides some workflow management capabilities and can be used for instance for :
- Incident/problem/change management
- Task / action follow-up

Why not try Ice3 Online Collaboration? It has wikis, blogs, document management, forums, project tasks, events, shared calendars, and unlimited work spaces where folks can work together. International timezone support makes it perfect for working with partners across the globe.

Oh, and yes, I have to declare an interest - it is provided by my company, but ultimately it is your choice :)